In general, the use of stoves for the purpose of space heating, such as residences and small businesses, is well known. Such heating devices are generally referred to as wood stoves and are available in a wide variety of configurations and designs. They may take the form of an actual stove-like device or a fireplace insert and are typically located inside the residence or other area to be heated. These stoves typically burn conventional firewood or pelletized fuel. The pelletized fuel may be made from different types of biomass, including sawdust, wood chips, different grasses, etc. In such wood stoves, the fuel is actually burned in a separate chamber or burner within the stove itself.
Such biomass fuel, including pellets, has also been used in gasifier technology, in which the biomass fuel input is used to produce fuel gas and carbon. Included in gasifier technology in general is the process of pyrolysis reduction, which basically is a chemical reduction of a selected biomass input in the absence of a flame. Pyrolysis generally is a controlled, relatively efficient process for producing fuel gas from a selected input. U.S. Pat. No. 4,421,524, in the name of Chittick and U.S. Pat. No. 4,530,702 in the name of Fetters et al, disclose pyrolysis gasifiers and the contents thereof are hereby incorporated by reference.
The use of a pyrolysis gasifier using a pelletized biomass input as part of a heating stove system would appear to have certain advantages, but heretofore, such a combination has not been particularly practical, due to the lack of automatic control of the operation of the combination apparatus from a thermostat. While a pyrolysis gasifier is capable of accommodating a wide variety of inputs, it heretofore has been primarily used to produce relatively large quantities of fuel gas on a steady state operation basis, particularly for power applications. Typically a human operator has been required to periodically monitor the operation of the gasifier. Such systems which are subject to a varying demand in particular have required relatively regular observation by a skilled operator.
Accordingly, the inability to automatically control a pyrolysis gasifier, so as to satisfy a variable demand, has substantially prevented the use of such gasifiers in applications such as space heating. The present invention is directed toward solving these problems and providing, in the preferred embodiment, a practical, thermostat controlled space heating apparatus using a pyrolysis-type gasifier which accommodates a variable demand.